MFC v6 and v7 has no register to read min scratch buffer size, so it has
to be read conditionally only if hardware supports it. This fixes following
NULL pointer exception on SoCs with MFC v6/v7:

8<--- cut here ---
Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = f25837f9
[00000000] *pgd=bd93d835
Internal error: Oops: 17 [#1] PREEMPT SMP ARM
Modules linked in: btmrvl_sdio btmrvl bluetooth mwifiex_sdio mwifiex ecdh_generic ecc
Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
PC is at s5p_mfc_get_min_scratch_buf_size+0x30/0x3c
LR is at s5p_mfc_get_min_scratch_buf_size+0x28/0x3c
...
[<c074f998>] (s5p_mfc_get_min_scratch_buf_size) from [<c0745bc0>] (s5p_mfc_irq+0x814/0xa5c)
[<c0745bc0>] (s5p_mfc_irq) from [<c019a218>] (__handle_irq_event_percpu+0x64/0x3f8)
[<c019a218>] (__handle_irq_event_percpu) from [<c019a5d8>] (handle_irq_event_percpu+0x2c/0x7c)
[<c019a5d8>] (handle_irq_event_percpu) from [<c019a660>] (handle_irq_event+0x38/0x5c)
[<c019a660>] (handle_irq_event) from [<c019ebc4>] (handle_fasteoi_irq+0xc4/0x180)
[<c019ebc4>] (handle_fasteoi_irq) from [<c0199270>] (generic_handle_irq+0x24/0x34)
[<c0199270>] (generic_handle_irq) from [<c0199888>] (__handle_domain_irq+0x7c/0xec)
[<c0199888>] (__handle_domain_irq) from [<c04ac298>] (gic_handle_irq+0x58/0x9c)
[<c04ac298>] (gic_handle_irq) from [<c0101ab0>] (__irq_svc+0x70/0xb0)
Exception stack(0xe73ddc60 to 0xe73ddca8)
...
[<c0101ab0>] (__irq_svc) from [<c01967d8>] (console_unlock+0x5a8/0x6a8)
[<c01967d8>] (console_unlock) from [<c01981d0>] (vprintk_emit+0x118/0x2d8)
[<c01981d0>] (vprintk_emit) from [<c01983b0>] (vprintk_default+0x20/0x28)
[<c01983b0>] (vprintk_default) from [<c01989b4>] (printk+0x30/0x54)
[<c01989b4>] (printk) from [<c07500b8>] (s5p_mfc_init_decode_v6+0x1d4/0x284)
[<c07500b8>] (s5p_mfc_init_decode_v6) from [<c07230d0>] (vb2_start_streaming+0x24/0x150)
[<c07230d0>] (vb2_start_streaming) from [<c0724e4c>] (vb2_core_streamon+0x11c/0x15c)
[<c0724e4c>] (vb2_core_streamon) from [<c07478b8>] (vidioc_streamon+0x64/0xa0)
[<c07478b8>] (vidioc_streamon) from [<c0709640>] (__video_do_ioctl+0x28c/0x45c)
[<c0709640>] (__video_do_ioctl) from [<c0709bc8>] (video_usercopy+0x260/0x8a4)
[<c0709bc8>] (video_usercopy) from [<c02b3820>] (do_vfs_ioctl+0xb0/0x9fc)
[<c02b3820>] (do_vfs_ioctl) from [<c02b41a0>] (ksys_ioctl+0x34/0x58)
[<c02b41a0>] (ksys_ioctl) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xe73ddfa8 to 0xe73ddff0)
...
---[ end trace 376cf5ba6e0bee93 ]---
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>